xrandr weirdness: cannot find crtc

[Alex Deucher]

On Thu, Jun 18, 2009 at 1:51 AM, Gilad Arnold<arnold at cs.berkeley.edu> wrote:
> Thanks, Alex.
>
> On Wed, Jun 17, 2009 at 12:22:59PM +1000, Alex Deucher wrote:
>> On Wed, Jun 17, 2009 at 3:28 AM, Gilad Arnold<arnold at cs.berkeley.edu> wrote:
>> > $ xrandr
>> > Screen 0: minimum 320 x 200, current 1400 x 1050, maximum 1920 x 1200
>> > VGA-0 connected 1400x1050+0+0 (normal left inverted right x axis y axis) 546mm x 352mm
>> >   1920x1200      60.0 +   60.0
>> >   1600x1200      75.0     70.0     65.0     60.0     60.0
>> >   1680x1050      60.0
>> >   1600x1000      60.0
>> >   1400x1050      74.8     60.0*
>> >   1280x1024      85.0     75.0     60.0
>> >   1280x960       85.0     60.0     60.0
>> >   1152x864       75.0
>> >   1024x768       85.0     75.1     75.0     70.1     60.0
>> >   832x624        74.6
>> >   800x600        85.1     72.2     75.0     60.3     56.2
>> >   640x480        85.0     75.0     72.8     75.0     60.0     59.9
>> >   720x400        85.0     70.1
>> >   640x400        85.1
>> >   640x350        85.1
>> > DVI-0 connected 1400x1050+0+0 (normal left inverted right x axis y axis) 546mm x 352mm
>> >   1920x1200      60.0 +
>> >   1600x1200      60.0     60.0
>> >   1680x1050      60.0
>> >   1600x1000      60.0
>> >   1400x1050      74.8     60.0*
>> >   1280x1024      85.0     75.0     60.0
>> >   1280x960       85.0     60.0     60.0
>> >   1152x864       75.0
>> >   1024x768       85.0     75.1     75.0     70.1     60.0
>> >   832x624        74.6
>> >   800x600        85.1     72.2     75.0     60.3     56.2
>> >   640x480        85.0     75.0     72.8     75.0     60.0     59.9
>> >   720x400        85.0     70.1
>> >   640x400        85.1
>> >   640x350        85.1
>> > LVDS connected 1400x1050+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
>> >   1400x1050      50.0*+
>> >   1280x1024      59.9     60.0
>> >   1280x960       60.0     59.9
>> >   1280x854       59.9
>> >   1280x800       59.8
>> >   1280x720       59.9
>> >   1152x768       59.8
>> >   1024x768       60.0     59.9
>> >   800x600        60.3     59.9     56.2
>> >   640x480        59.9     59.4
>> > S-video disconnected (normal left inverted right x axis y axis)
>>
>> When the one crtc drives several monitors the mode timing must be the
>> identical on both. I suspect the mode timings aren't quite the same
>> across monitors for the modes you are trying to set.
>
> Looks like at least the mode I tested with explicitly, 1680x1050, has
> the same timing rates (60.0). I believe (not tested right now, not in
> front of the external monitor) that I can actually activate both VGA-0
> and DVI-0 at any mode (on the same rate) if I turn one off, set the
> other to the desired mode, then set the first one to the same mode.
> I can test if you like.

You'll have to look at the actual mode lines (xrandr --verbose) to see
is they are really indentical.  If the modes are indentical you should
be able to drive both heads using the same crtc.  You can use the
--crtc option with xrandr to force which crtc you want to drive a
particular output.

>
>> Alternatively, xrandr isn't being smart about how it sets the mode
>> which results in the error.
>
> If this is the case, where should I report this?

https://bugs.freedesktop.org

Alex